Aberrant Mark of Madness is a Dragonmark feat. The dragonmarks are used in the Eberron campaign setting.
Abeerrant marks are more common amongs the races that have dragonmarked houses, although a member of any race can bear one, but they are still rare.
A character can only have one Dragonmark feat.
Benefit: Whenever you hit an enemy with a daily attack power, that enemy takes a -1 penalty to attack rolls against you until the end of the encounter. This is a fear effect. [EPG:86]